AN3254 datasheet(20/24 Pages) STMICROELECTRONICS

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Converting readings into measured values

AN3254

20/24

Doc ID 17783 Rev 1

Line frequency is calculated as follows:

frequency = Fm /( x_period * 2

The integrator and differentiator gains are calculated as follows:

Kint = 2 * x_period * 2

5/ (p * 216)

Kdif = 1/ (2 * Kint)

Typical values for these gains are:

Table 4.

STPMC1 internal parameters value

Parameter

Value

Meaning

0,875

Voltage calibrator ideal value if PM = 0 (1)

0,9375

Voltage calibrator ideal value if PM = 1

0,875

Current calibrator ideal value if PM = 0

0,9375

Current calibrator ideal value if PM = 1

Kisum

0,875

Calibrator ideal value for sI RMS (sum of currents)(2)

Voltage channel gain

len_i

216

Current register length

len_u

212

Voltage register length

len_isum

212

sI RMS (sum of currents) register length

Kint_comp

1,004

Gain of decimation filter

3.14159

4 * 106

If oscillator frequency is 4.000 or 8.000 MHz

222

If oscillator frequency is 4.194 or 8.388 MHz

4915200

If oscillator frequency is 4.915 or 9.830 MHz

Kut

For CT/Shunt

For Rogowski coil

Vref

1.23

Internal voltage reference

PM is CFG 21, it sets the meter precision (Class 1 or Class 0.1)

12 bits in DMN register

Table 5.

Kint and Kdif typical values

Kdif

0,6135

Gain of differentiator @ line frequency = 50 Hz

0.7359

Gain of differentiator @ line frequency = 60 Hz

Kint

0,815

Gain of integrator @ line frequency = 50 Hz

0.679

Gain of integrator @ line frequency = 60 Hz

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